1. The Field of the Invention
This invention relates to novel, improved erasable systems including a marking element providing a marking surface and erasable marking compositions for applying markings to such surfaces. 2. Description of the Prior Art
Erasable systems including a marking element carrying or providing a marking surface and an erasable ink marking composition for applying markings to the marking surface are known to the art. Essentially, such known systems include a marking element comprising a substrate carrying an impervious or substantially non-porous marking surface and an erasable ink marking composition for applying markings to the surface which can be erased from the surface by wiping the surface with a dry eraser such as a cloth or paper tissue. The idealized combination of performance characteristics for known erasable systems has been reasonably well defined. The defined desired combination of performance characteristics for a marking element includes the capability of the marking surface to effectively receive, retain, and display applied marking composition until the received marking is erased from the surface without leaving any significant residual visable evidence of the received marking. Additionally, the desired combination of performance characteristics for marking compositions of erasable systems includes the capability of the marking composition to deposit uniform, visible markings on the surface which can dry rapidly to provide a film or coalesced residue which can be substantially completely erased from the marking surface without leaving any remaining evidence of colorants or other ingredients of the marking comPosition on the surface.
A known erasable system is disclosed in commonly assigned U.S. Patents 3,834,823 and 3,949,132. The erasable system disclosed in these patents includes a marking element carrying a smooth, hard, virtually impervious marking surface such as a hard, plastic surface. The erasable marking composition of the disclosed system is included in a writing instrument having a porous point such as a felt point or a point composed of synthetic or natural fibers bound together to provide capillary channels. Essential ingredients of the erasable marking composition include a release agent having a very low vapor pressure, water, a colorant which is soluble in the water but insoluble in the release agent and a silicone surfactant which is soluble in the marking composition. Additional ingredients- which may be included in the marking composition are a water-soluble wax and a water-miscible organic solvent.
In practice, the marking composition is applied to the marking surface and during evaporation of the aqueous or partially aqueous solvent, the release agent comes out of solution to form a film on the marking surface. Accordingly, on drying, the trace or line provided by the marking composition includes colorants which are insoluble in the release agent, and the colorants lie on top of the thin film of release agent. In this way, the film of release agent provides a barrier between the film and the marking surface -: so that the film can be erased from the surface without leaving any residual visible evidence of the marking on the surface.
U.S. Patent 3,563,782 describes another known erasable system in which the marking surface is the surface of a pigmented plastic substrate, and the erasable marking composition consists of a dispersion of dye particles in a solvent having a low surface tension. The marking composition is applied to the marking surface, and after evaporation of the solvent, an erasable, non-continuous film is provided on the marking surface and the film includes discrete, closely spaced dye particles The non-continuous film of dye particles can be erased from the marking surface by wiping the film with a cloth or soft paper.
The erasable systems described above are especially , adaptable for use as substitutes for blackboards, and the marking elements usually takes the form of a relatively large panel. Moreover, the markings provided on the marking surface of the above-described erasable systems have little rub resistance so that the markings can be completely erased from the surface by a dry cloth or felt eraser to provide a clean marking surface on the marking element. Known erasable systems Providing markings on a marking surface having good rub resistance require cloths or paper wet with water or solvent to effectively remove such markings and provide a clean surface for new markings. The use of wet cloths or paper obviously complicates the achievement of a clean surface for new markings.
Additionally, known erasable systems are not so easily or readily adaptable for use in office or desk paraphernalia such as daily calendars or desk notebooks designed to record appointments, schedules, accounts, or similar notations An erasable system for use in such paraphernalia requires significantly different performance characteristics from those required for erasable systems used as substitutes for blackboards. For example, such paraphernalia is normally designed for individuals for recording desired notations useful to the individual Accordingly, the size of the marking element needed is relatively small, and preferably, the element should be relatively flexible and have qualities and properties more closely corresponding to paper rather than to plastics. Moreover, the marking composition should be capable of reliably providing legible markings in relatively small areas of the marking surface. Also, the markings should have sufficient rub resistance so that they are not inadvertently erased such as by accidental rubbing or wiping or abrasion of the surface. The degree of rub resistance of the marking is particularly important in such paraphernalia involving a plurality of marking elements superposed on each other and where one or more of the elements has erasable markings on the marking surface. Ideally, the marking should be mechanically erasable by an elastomeric eraser rather than by a cloth or paper or the like. In this way, the marking can be effectively retained on the marking surface until it is no longer needed, and markings in selected areas can be completely and neatly erased without affecting markings in non-selected areas.
The present invention presents to the art novel, improved erasable systems having an especially des1able combination of performance characteristics which provide sufficient flexibility and latitude so that the systems are adapTable for use as a substitute for blackboards and also are especially adaptable for providing the above-described desk or office paraphernalia.